Redistribution layers for microfeature workpieces, and associated systems and methods

ABSTRACT

Redistribution layers for microfeature workpieces, and associated systems and methods are disclosed. One method for processing a microfeature workpiece system includes positioning a pre-formed redistribution layer as a unit proximate to and spaced apart from a microfeature workpiece having an operable microfeature device. The method can further include attaching the redistribution layer to the microfeature workpiece and electrically coupling the redistribution layer to the operable microfeature device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 13/236,372, filed Sep. 19, 2011, now U.S. Pat. No. 9,230,859, which is a divisional of U.S. application Ser. No. 11/513,661 filed Aug. 30, 2006, now U.S. Pat. No. 8,021,981, each of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure is directed to redistribution layers for microfeature workpieces, and associated systems and methods.

BACKGROUND

Microelectronic devices generally have a die (i.e., a chip) that includes integrated circuitry with a high density of very small components. In a typical process, a large number of dies are manufactured on a single wafer using many different processes that may be repeated at various stages (e.g., implanting, doping, photolithography, chemical vapor deposition, plasma vapor deposition, plating, planarizing, and etching). The dies typically include an array of very small bond-pads electrically coupled to the integrated circuitry. The bond-pads are external electrical contacts through which the supply voltage, signals, etc., are transmitted to and from the integrated circuitry. After forming the dies, the wafer is thinned by backgrinding, and then the dies are separated from one another (i.e., singulated) by dicing the wafer. Next, the dies are “packaged” to couple the bond-pads to a larger array of electrical terminals that can be more easily coupled to the various power supply lines, signal lines, and ground lines. Conventional processes for packaging dies include electrically coupling the bond-pads on the dies to an array of leads, ball-pads, or other types of electrical terminals, and then encapsulating the dies to protect them from environmental factors (e.g., moisture, particulates, static electricity, and physical impact).

Different types of dies may have widely different bond pad arrangements, and yet should be compatible with similar external devices. Accordingly, existing packaging techniques can include forming a redistribution layer (RDL) on the die. The RDL includes lines and/or vias that connect the die bond pads with RDL bond pads, which are in turn arranged to mate with the bond pads of external devices. The RDL is typically formed directly on the die using deposition and lithography techniques.

One drawback with the foregoing RDL formation technique is that it may not be an economical process for certain types of dies. For example, imager dies typically include image sensors on the front side of the die and bond pads positioned on the back side of the die, so that connections to the bond pads do not interfere with the operation of the image sensors. However, the lithography techniques and other conventional semiconductor processes employed for forming RDLs are typically performed on the front side of the die, and adjusting these techniques to provide for the proper alignment of features on the back side of the die can require special tooling and/or techniques that increase the cost of forming the RDL. Accordingly, there is a need for lower cost RDL formation techniques that may be applicable to a wide variety of die types.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partially schematic illustration of a representative microfeature workpiece carrying microfeature dies configured in accordance with embodiments of the invention.

FIG. 1B is a schematic illustration of a microfeature die singulated from the workpiece shown in FIG. 1A.

FIG. 1C is a schematic illustration of a system that can include one or more microfeature dies in accordance with embodiments of the invention.

FIG. 1D is a partially schematic, cross-sectional illustration of a portion of a workpiece package after the formation of conductive structures, including a redistribution layer, in accordance with an embodiment of the invention.

FIGS. 2A-2L illustrate a process for forming a conductive via used to electrically couple a microfeature workpiece to a redistribution layer in accordance with an embodiment of the invention.

FIGS. 3A-3C illustrate a process for forming a microfeature workpiece having a redistribution layer in accordance with an embodiment of the invention.

FIG. 4 illustrates a portion of a microfeature assembly that includes the microfeature workpieces shown in FIGS. 2L and 3C, joined in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1A is a microfeature workpiece 100 in the form of a wafer 170 that includes multiple microfeature dies 120. At least some of the processes described below may be conducted on the microfeature workpiece 100 at the wafer level, and other processes may be conducted on the individual microfeature dies 120 of the microfeature workpiece 100 after the dies 120 have been singulated from the larger wafer 170. Accordingly, unless otherwise noted, structures and methods described below in the context of a “microfeature workpiece” can apply to the wafer 170 and/or the dies 120 that are formed from the wafer 170.

As used herein, the terms “microfeature workpiece” and “workpiece” refer to substrates in and/or on which microelectronic devices are integrally formed. Typical microelectronic devices include microelectronic circuits or components, thin-film recording heads, data storage elements, microfluidic devices, and other products. Micromachines and micromechanical devices are included within this definition because they are manufactured using much of the same technology that is used in the fabrication of integrated circuits. Substrates can be semiconductive pieces (e.g., doped silicon wafers or gallium arsenide wafers), non-conductive pieces (e.g., various ceramic substrates), or conductive pieces. In some cases, the workpieces are generally round, and in other cases, the workpieces have other shapes, including rectilinear shapes.

FIG. 1B is a schematic illustration of an individual die 120 after it has been singulated from the wafer 170 shown in FIG. 1A. The die 120 can include operable microelectronic structures, optionally encased within a protective encapsulant. Pins, bond pads, solder balls, and/or other conductive structures provide electrical communication between structures within the die 120 and structures/devices located external to the die.

Individual dies may be incorporated into any of a myriad of larger and/or more complex systems 180, a representative one of which is shown schematically in FIG. 1C. The system 180 can include a processor 181, a memory 182, input/output devices 183, and/or other subsystems or components 184. Microfeature workpieces (e.g., in the form of microfeature dies and/or combinations of microfeature dies) may be included in any of the components shown in FIG. 1C. The resulting system 180 can perform any of a wide variety of computing, processing, storage, sensor and/or other functions. Accordingly, representative systems 180 include, without limitation, computers and/or other data processors, for example, desktop computers, laptop computers, Internet appliances, hand-held devices (e.g., palm-top computers, wearable computers, cellular or mobile phones, multi-processor systems, processor-based or programmable consumer electronics, network computers, mini computers). Other representative systems 180 include cameras, light sensors, servers and associated server subsystems, display devices, and/or memory devices. Components of the system 180 may be housed in a single unit or distributed over multiple, interconnected units, e.g., through a communications network. Components can accordingly include local and/or remote memory storage devices, and any of a wide variety of computer-readable media, including magnetic or optically readable or removable computer disks.

Several embodiments of microfeature workpieces having redistribution layers (RDLs) and associated methods are described below. In particular embodiments, the RDL is formed in a separate microfeature workpiece, which is then attached to a microfeature workpiece having operable microfeature devices. A person skilled in the relevant art will understand, however, that the invention may have additional embodiments, and that the invention may be practical without several of the details of the embodiments described below with reference to FIGS. 1D-4.

FIG. 1D is a partially schematic, side elevation view of a package 150 formed from a first microfeature workpiece 100 and a second microfeature workpiece 200, in accordance with an embodiment of the invention. Many components shown in FIG. 1D are shown schematically for purposes of illustration. These components (and others) are shown and described in greater detail later with reference to additional Figures. In the illustrated embodiment, the second microfeature workpiece 200 includes an operable microfeature device 218, while the first microfeature workpiece 100 does not. Instead, the first microfeature workpiece 100 includes a redistribution layer (RDL) 160 that is configured to reroute signals to and/or from the second microfeature workpiece 200. Accordingly, the first microfeature workpiece 100 can include a first bond site 119, and a conductive structure 162 connected to the first bond site 119. The conductive structure 162 can include a lateral line 163 connected to an RDL bond site 161 that is laterally offset from the first bond site 119. The RDL bond site 161 can support a conductive coupler 152 (e.g., a solder ball) that provides electrical communication with external devices.

The first microfeature workpiece 100 can include a first interconnect structure 117 that is connected to a corresponding second interconnect structure 217 of the second microfeature workpiece 200. The second interconnect structure 217 is connected to a second bond site 219, that is in turn connected to the microfeature device 218 by a conductive line 216. An optional covering 151 (e.g., a mold compound or underfill material) can be disposed over the first and second bond sites 119, 219, leaving the RDL (or third) bond site 161 exposed. In other embodiments, one or both of the first and second bond sites 119, 219 can be exposed for connections to other structures, including but not limited to stacked microfeature workpieces.

The first microfeature workpiece 100 and the second microfeature workpiece 200 can be processed independently (e.g., in parallel or sequentially) and can then be attached to each other to provide for redistribution of electrical signals received from and delivered to the second microfeature workpiece 200. Accordingly, the first microfeature workpiece 100 need not include any operable microfeature devices. As will be discussed in greater detail below, this can provide the manufacturer with increased flexibility when selecting processes for forming the redistribution layer 160.

Further details of the formation of the second microfeature workpiece 200, which includes at least one operable microfeature device 218, are described below with reference to FIGS. 2A-L. Further details of the formation of the first microfeature workpiece 100, which includes the RDL 160, are described below with reference to FIGS. 3A-3C. Representative processes for attaching the microfeature workpieces 100, 200 are then described with reference to FIG. 4.

FIG. 2A is a side cross-sectional view of a portion of the second workpiece 200 prior to the formation of a conductive interconnect structure in accordance with an embodiment of the invention. The workpiece 200 can include a substrate 201 having a first side or surface 202 and a second side or surface 203. An integrated circuit or other operable microfeature device 218 is formed in and/or on the substrate 201, e.g., at or near the first side 202. As used herein, the term “operable microfeature device” refers generally to a device that has a function beyond that of a simple conductor. Such devices can accordingly include integrated circuits, capacitors, and/or sensing elements, but do not include bond pads, conductive lines, or vias.

The operable microfeature device 218 is coupled to the second bond site 219 (which can include a bond pad or other terminal) with a coupler 216. The second bond site 219 shown in FIG. 2A is an external feature at the first side 202 of the substrate 201. In other embodiments, however, the second bond site 219 can be an internal feature that is embedded at an intermediate depth within the substrate 201.

First and second dielectric layers 204 and 205 (e.g., passivation layers or other insulating layers) can be located at the first side 202 to protect the underlying substrate 201. As shown in FIG. 2A, the second dielectric layer 205 has been patterned and etched to expose the second bond site 219. A mask 206 is applied over the second dielectric layer 205 and patterned. The mask 206 can be a layer of resist that is patterned according to the arrangement of second bond sites 219 on the substrate 201. Accordingly, the mask 206 can have an opening over each second bond site 219.

Referring next to FIG. 2B, a via 230 has been formed in the workpiece 200 so as to extend along a generally straight axis into the substrate 201 through the second bond site 219 and the first surface 202. The via 230 can be formed using any of a variety of techniques, including etching or laser drilling. The via 230 can be a blind via, as shown in FIG. 2B, e.g., a via that does not extend entirely through the workpiece 200 and/or the substrate 201. In other embodiments, the via 230 can extend entirely through the workpiece 200 and/or the substrate 201, as indicated by dashed lines in FIG. 2B. Further details of representative methods for forming the via 230 are disclosed in pending U.S. Patent Application Publication No. 2006/0290001, which is incorporated herein by reference. A third dielectric layer 232 (e.g., a passivation layer or other insulating layer) is deposited onto the workpiece 200 to line the sidewalls 231 of the via 230 within the substrate 201. The third dielectric layer 232 electrically insulates components in the substrate 201 from an interconnect structure that is subsequently formed in the via 230.

Referring to FIG. 2C, a suitable etching process (e.g., a spacer etch) is used to remove the third dielectric layer 232 at all horizontal positions while leaving it intact at all vertical positions, e.g., along the via sidewall. Accordingly, at least part of the second bond site 219 can be exposed for electrical coupling to conductive structures in the via 230, as is described in greater detail below.

FIG. 2D illustrates the second workpiece 200 after a conductive barrier layer 233 has been deposited over the third dielectric layer 232 so as to be in electrical contact with the second bond site 219. The barrier layer 233 generally covers the second dielectric layer 205 and the second bond site 219 in addition to the third dielectric layer 232. In one embodiment, for example, the barrier layer 233 is a layer of tantalum that is deposited onto the second workpiece 200 using a physical vapor deposition (PVD) process. The thickness of the barrier layer 233 can be about 150 Angstroms. In other embodiments, the barrier layer 233 may be deposited onto the second workpiece 200 using other vapor deposition processes, such as chemical vapor deposition (CVD), and/or may have a different thickness. The composition of the barrier layer 233 is not limited to tantalum, but rather may be composed of tungsten or other suitable materials.

Referring next to FIG. 2E, a seed layer 234 is deposited onto the barrier layer 233. The seed layer 234 can be deposited using vapor deposition techniques, such as PVD, CVD, atomic layer deposition, and/or plating. The seed layer 234 can be composed of copper or other suitable materials. The thickness of the seed layer 234 may be about 2000 Angstroms, but can be more or less depending upon the depth and aspect ratio of the via 230. In several embodiments, the seed layer 234 may not uniformly cover the barrier layer 233, such that the seed layer 234 has voids 235 within the via 230. This can cause non-uniform electroplating in the via 230 and across the workpiece 200. When the seed layer 234 is deficient, it may be enhanced using a process that fills voids or noncontinuous regions of the seed layer 234 to form a more uniform seed layer. Referring to FIG. 2F, for example, voids 235 and/or noncontinuous regions of the seed layer 234 have been filled with additional material 236, such as copper or another suitable material. One suitable seed layer enhancement process is described in U.S. Pat. No. 6,197,181, which is incorporated by reference.

Referring next to FIG. 2G, a resist layer 207 is deposited onto the seed layer 234 and is patterned to have an opening 208 over the second bond site 219 and the via 230. A conductive lining or layer 237 is then deposited onto the exposed portions of the seed layer 234 in the via 230. The conductive lining 237 can include copper that is deposited onto the seed layer 234 in an electroless plating operation, or an electroplating operation, or by another suitable method. Optionally, the conductive lining 237 can be formed from multiple overlaid layers, but for purposes of illustration, a single layer is shown in FIG. 2G. After the conductive lining 237 has been formed, a central opening 238 typically remains in the via 230.

FIG. 2H illustrates the second microfeature workpiece 200 after a fill material 239 has been introduced into the opening 238. The fill material 239 can include solder or an electrically conductive polymer in one embodiment and/or other constituents in other embodiments. In particular embodiments, the fill material 239 can be less conductive than the conductive liner 237. For example, in some embodiments, the fill material 239 need not be electrically conductive at all, if other constituents in the via 230 are sufficiently conductive. Accordingly, in any of these embodiments, one or more of the fill material 239 and other materials in the via 230 (e.g., the barrier layer 233, the seed layer 234, and the conductive lining 237) form the electrically conductive second interconnect structure 217.

In FIG. 2I, the resist layer 207 shown in FIG. 2H has been removed from the second microfeature workpiece 200. Alternatively, the resist layer 207 can be removed prior to introducing the fill material. In FIG. 2J, the second surface 203 of the second microfeature workpiece 200 has been ground back to expose the end of the second interconnect structure 217. In the illustrated embodiment, sufficient material is removed from the second surface 203 to expose the fill material 239 within the via 230. In other embodiments, less material can be removed, so that the conductive lining 237, or other conductive constituents toward the bottom of the via 230 are exposed. In addition to exposing conductive materials in the via 230, backgrinding also reduces the overall thickness of the second microfeature workpiece 200. For example, the second microfeature workpiece 200 can have a thickness of about 50-60 μ (or more or less) after backgrinding.

As shown in FIG. 2K, additional material may be removed from the second surface 203 of the substrate material 201, without removing corresponding material from the interconnect structure 217. For example, a plasma etchback process can be used to remove only the substrate material 201. As a result, the interconnect structure 217 can include a protrusion or stud 240 that extends beyond the second surface 203 of the substrate 201. In particular embodiments, the protrusion 240 can extend 5-15 μ beyond the surrounding second surface 203 and in other embodiments, this distance can be different. The protrusion 240 can form a connection region that facilitates an electrical connection with the corresponding interconnect structure of the first microfeature workpiece 100 (FIG. 1D), as is discussed in further detail later with reference to FIG. 4.

In FIG. 2L, the second workpiece 200 is prepared for being connected to the first microfeature workpiece 100 (FIG. 1D). An optional conductive cap 241 is positioned at the end of the conductive protrusion 240. The conductive cap 241 can include copper, nickel, gold or another conductive material that can facilitate electrical connectivity with the corresponding interconnect structure of the first microfeature workpiece 100. A substrate adhesive 242 is then disposed over the second surface 203 of the substrate 201. In a particular process, the substrate adhesive 242 is spun onto the substrate 201 to a depth that does not cover the protrusion 240 and the (optional) conductive cap 241. In another embodiment, a spin-on process or other process is used to dispose the substrate adhesive 242 over the cap 241, and a subsequent selective removal process is then used to remove the adhesive from the cap 241. For example, a plasma etchback process can be used to remove any overlying substrate adhesive 242. In at least some cases, it may be beneficial to avoid disposing the substrate adhesive 242 over the cap 241, to reduce the likelihood of contaminating the cap 241 with residual adhesive. Accordingly, in at least some cases, the substrate adhesive 242 can be applied with a translating x-y nozzle programmed to deposit the substrate adhesive 242 over portions of the second microfeature workpiece surface not occupied by the second interconnect structure 217. The substrate adhesive 242 will be used to form a generally permanent bond with the first microfeature workpiece 100. Accordingly, the substrate adhesive 242 can include a thermoset material (e.g., an epoxy underfill material) of other suitable long-term bonding agent.

The second microfeature workpiece 200 can optionally be supported by a carrier 243, for example, if the second microfeature workpiece 200 is thin (as it typically will be) and/or otherwise fragile. The carrier 243 can be temporarily attached to the second microfeature workpiece 200 with a carrier adhesive 244. The carrier adhesive 244 can include a thermoplastic material or other material that provides a sufficiently strong bond to allow the carrier 243 and the second microfeature workpiece 200 to be moved as a unit, but is also releasable after the second microfeature workpiece 200 has been packaged. The carrier 243 can include any of a variety of suitable devices, including a film frame, and can be attached to the second microfeature workpiece 200 after backgrinding (as shown in FIG. 2L) or before backgrinding.

FIGS. 3A-3C illustrate a representative process for forming an interconnect structure and redistribution layer in the first microfeature workpiece 100. Many aspects of this process are well-known and/or generally similar to the processes described above with reference to FIGS. 2A-2L, and accordingly are not discussed in great detail below.

Beginning with FIG. 3A, the first microfeature workpiece 100 can include a substrate 101 that does not include microfeature devices. For example in a particular embodiment, the substrate 101 can include a bare silicon wafer or wafer portion, that is undoped. In other embodiments, the substrate 101 can include various treatments (e.g., doping), but does not include capacitors, memory devices, processor devices, or other operable microfeature devices. Instead, as discussed above with reference to FIG. 1D, the first microfeature workpiece 100 includes the redistribution layer 160. The redistribution layer 160 in turn can include a first dielectric layer 104 disposed on a first surface 102 of the substrate 101, and the conductive structure 162 disposed on the first dielectric layer 104. A second dielectric layer 105 can be disposed over the conductive structure 162 and can then be selectively patterned to expose particular conductive sections. These conductive sections can include the first bond site 119 and the third or RDL bond site 161. A connecting lateral line 163 is located beneath the second conductive layer 105 to connect the first bond site 119 and the third bond site 161. The conductive structure 162 can be formed from aluminum, copper and/or any other suitable conductive material.

Conventional processes that are typically used to form RDLs on microfeature workpieces with operable microfeature devices can be used to form the RDL 160 shown in FIG. 3A. For example, the conductive structure 162 can be formed from aluminum that is applied in a sputtering process, under vacuum. The conductive structure 162 can accordingly rely on the underlying substrate material for physical support. However, as described in greater detail later, these processes may be modified for enhanced efficiency and/or throughput, at least in part because the first microfeature workpiece 100 need not include operable microfeature devices.

FIG. 3B illustrates the first microfeature workpiece 100 after the first interconnect structure 117 has been formed at the first bond site 119. The steps used to form the first interconnect structure 117 are generally similar to those discussed above with reference to the formation of the second interconnect structure 217 shown in FIGS. 2A-2L. Accordingly, the first interconnect structure 117 can include a via 130 having (in sequence) a dielectric layer 132, a barrier layer 133, a seed layer 134, a conductive liner 137 disposed on the seed layer 134, and a fill material 139 that fills the remaining volume of the via 13.

FIG. 3C illustrates the first microfeature workpiece 100 after material has been removed from a second surface 103 to expose a protrusion 140 of the first interconnect structure 117. The first microfeature workpiece can have a thickness of 50-60 μ (or more or less) after backgrinding. An optional conductive cap 141 can be positioned on the exposed protrusion 140, and an adhesive layer 142 can be disposed on the second surface 103. Because the first microfeature workpiece 100 is typically very thin, it can be supported by an optional carrier 143 attached to the substrate 101 with a carrier adhesive 144. The first microfeature workpiece 100 is now ready for joining with the second microfeature workpiece 200.

FIG. 4 illustrates a process for joining the first microfeature workpiece 100 and the second microfeature workpiece 200. In the illustrated embodiment, the first microfeature workpiece 100 has been inverted from the orientation shown in FIG. 3C, while the second microfeature workpiece 200 has the same orientation shown in FIG. 2L. The joining process can in some embodiments be completed at the die level (e.g., on singulated portions of the first and second workpieces 100, 200) and in other embodiments, at the wafer level, or at an intermediate level. Performing these processes at the wafer level may have significant cost advantages over performing the processes at the die level. In any of these embodiments, the first and second microfeature workpieces 100, 200 are oriented so that the corresponding substrate adhesives 142, 242 face toward each other, and the corresponding interconnect structure protrusions 140, 240 are aligned with each other. An existing alignment tool can be used to properly align the interconnect structures 117, 217 and the corresponding protrusions 140, 240. Such tools can rely on infrared light that penetrates through the workpieces 100, 200, or individual cameras located proximate to each workpiece 100, 200. Suitable existing bonding and alignment systems are available from, among other sources, Suss MicroTec of Munich, Germany. The microfeature workpieces 100, 200 are then brought toward each other (e.g., stacked) so that the opposing conductive caps 141, 241 contact each other, and the opposing substrate adhesives 142, 242 also contact each other.

The assembly can undergo further processing to complete the electrical and physical connections between the two microfeature workpieces 100, 200. For example, the microfeature workpieces 100, 200 can undergo an elevated temperature and/or elevated pressure process to complete, cure or otherwise improve the connection between the two substrate adhesives 142, 242 and/or between the two caps 141, 241. For example, an elevated temperature process can be used to cure the substrate adhesives 142, 242 and/or establish a cohesive intermetallic bond between the two end caps 141, 241. If the end caps 141, 241 are not included in the assembly, the elevated temperature process can facilitate or improve an intermetallic bond between other constituents of the interconnect structure 117, 217 (e.g., between the fill materials 139, 239, and/or between the conductive liners 137, 237). For example, if the fill materials 139, 239 include solder, the elevated temperature process can include reflowing or melting the solder to join the two interconnect structures 117, 217.

Once the attachment process has been completed, the optional carriers 143, 243 can be removed by releasing the corresponding adhesives 144, 244. The resulting package 150 is generally similar to that shown and discussed above with reference to FIG. 1D. The overall thickness of the resulting package can be on the order of 100 μ (or more or less), with specific package thicknesses being dependent upon the individual thicknesses of the first and second microfeature workpieces 100, 200. The package 150 can be attached to external devices (e.g., printed circuit boards). The packages 150 can also be stacked, one upon the other, with the RDL 160 providing signal routing between the stacked packages.

Particular embodiments of the foregoing methods can include positioning a pre-formed redistribution layer as a unit proximate to and spaced apart from a microfeature workpiece having an operable microfeature device, attaching the redistribution layer to the microfeature workpiece, and electrically coupling the redistribution layer to the operable microfeature device. Accordingly, such methods can result in improved processes and microelectronic packages. For example, the redistribution layer or RDL can be formed as a stand-alone unit (e.g., in or on the first microfeature workpiece 100) prior to being attached to the second microfeature workpiece 200. Because the first microfeature workpiece 100 need not include functioning microfeature devices, the processes used to form the RDL need not be constrained by thermal budgets and/or other limitations typically associated with functioning microfeature devices. For example, the RDL can be formed using high temperature processes, which typically take less time and/or produce more consistent results than do lower temperature processes. Many of these processes can be performed on the first microfeature workpiece 100 while the first microfeature workpiece 100 has a significant thickness (e.g., before the back side of the first microfeature workpiece is ground back). As a result, the first microfeature workpiece 100 need not be attached to a carrier for many of the processes described above, and may only be attached to the carrier just prior to being attached to the second microfeature workpiece 200. This arrangement can simplify the process of handling the first microfeature workpiece 100 while the RDL is being formed. Still further, conventional techniques can be used to form the RDL. As a result, the manufacturer need not employ special tooling and/or other costly techniques that are typically associated with forming the RDL directly on the back side of a workpiece containing functioning microelectronic devices.

When forming redistribution layers directly on the back side or second side of the microfeature workpieces having operable devices, the microfeature workpiece is typically supported by a carrier that is attached to the workpiece with an adhesive. The releasable interface between the carrier and the workpiece may include gaps or voids filled with air, which can expand and burst or otherwise damage the workpiece during the vacuum processes that are typically used to form the RDL. However, using techniques generally similar to those described above, the foregoing vacuum process can be applied to the first microfeature workpiece 100 only, and applied at a point when the first microfeature workpiece 100 is thick enough not to require a carrier. Accordingly, the likelihood for causing damage to the die as a result of adhesive voids can be reduced or eliminated.

Conventional redistribution layers formed directly on a microfeature workpiece are typically formed toward the end of the fabrication process for that workpiece. Accordingly, the microfeature workpiece is at or close to its highest dollar value point. If the microfeature device is then damaged during the formation of the RDL, the dollar loss can be significant. Conversely, embodiments of the process described above include forming the RDL or a separate workpiece (e.g., the first workpiece). This arrangement can reduce the likelihood for damaging the product workpiece (e.g., the second workpiece). This arrangement can also increase the overall throughput for the end product because the RDL in the first workpiece can be formed in parallel with the operable microfeature devices in the second workpiece.

Certain aspects of the foregoing processes and resulting devices can be altered in other embodiments. For example, in some embodiments, the adhesive between the first microfeature workpiece 100 and the second microfeature workpiece 200 can be eliminated, and the bond between the first and second interconnect structures 117, 217 can be sufficient to hold the two workpieces together.

From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the invention. For example the end caps described above can be eliminated in some embodiments. The processes used to form the interconnect structures and/or connect the microfeature workpieces can be altered in some embodiments. In other embodiments, the first microfeature workpiece with the RDL can be applied to the first or device side of the second microfeature workpiece. Certain aspects of the invention described in the context of particular embodiments may be combined or eliminated in other embodiments. For example, in some embodiments, the first and second microfeature workpieces can be attached to each other using techniques other than face-to-face adhesive bonding (e.g., by using edge bonding). Further, while advantages associated with certain embodiments of the invention have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the invention. Accordingly, the invention is not limited except as by the appended claims. 

I claim:
 1. A semiconductor device assembly, comprising: a first semiconductor die including an integrated circuit and a conductive trace operably coupled to the integrated circuit; a second semiconductor die attached to the first die and having no integrated circuit; a first via connected to the conductive trace and extending through the first die; and a second via extending through the second die, wherein the first and second vias join with one another at a location between the first and second dies.
 2. The semiconductor device assembly of claim 1, further comprising a first conductive cap on the first via, and a second conductive cap on the second via and connected to the first conductive cap.
 3. The semiconductor device assembly of claim 1 wherein the second die comprises a silicon substrate and an adhesive material on an outer surface of the silicon substrate, wherein the adhesive material directly attaches the silicon substrate to the first die.
 4. The semiconductor device assembly of claim 3 wherein the first die comprises a semiconductor substrate, and an adhesive material on an outer surface of the semiconductor substrate and attached to the adhesive material of the second die.
 5. The semiconductor device assembly of claim 1 wherein the second via includes a protrusion projecting toward the first via and attached thereto.
 6. The semiconductor device assembly of claim 5 wherein the first via includes a protrusion attached to the protrusion of the second via.
 7. The semiconductor device assembly of claim 6, further comprising a conductive cap between the protrusion of the first die and the protrusion of the second die.
 8. The semiconductor device assembly of claim 1 wherein: the first die includes a first outer surface; the first via extends beyond the first outer surface; the second die includes a second outer surface facing the first outer surface; and the second via extends beyond the second outer surface.
 9. A semiconductor device assembly, comprising first and second semiconductor dies attached to one another and each including— a semiconductor substrate; a via extending entirely through the semiconductor substrate and attached to the via of the other die; and a conductive structure coupled to the via, wherein the first die includes an integrated circuit and the second die does not include an integrated circuit, and wherein the integrated circuit of the first die is electrically coupled to the via and the conductive structure of each of the first and second dies.
 10. The semiconductor device assembly of claim 9 wherein each semiconductor substrate comprises a silicon substrate, and wherein the integrated circuit is formed in the silicon substrate of the first die.
 11. The semiconductor device assembly of claim 9 wherein the semiconductor substrate of the second die comprises a bare silicon substrate.
 12. The semiconductor device assembly of claim 9 wherein the via of each of the first and second dies includes a protrusion projecting from an outer surface of the semiconductor substrate and attached to the protrusion of the other via.
 13. The semiconductor device assembly of claim 9 wherein each of the first and second dies further includes an adhesive material attached to the adhesive material of the other die.
 14. The semiconductor device assembly of claim 13 wherein each via is separated from the adhesive material of the other die.
 15. The semiconductor device assembly of claim 9, further comprising: a first conductive feature on the via of the first die; and a second conductive feature on the via of the second die, wherein the second conductive feature is connected to the first conductive feature at a location between the first and second vias.
 16. A semiconductor device package, comprising: a first semiconductor die including a semiconductor substrate and a plurality of first vias extending therethrough; and a second semiconductor die stacked on the first semiconductor die, the second semiconductor including a semiconductor substrate and a plurality of second vias extending therethough, wherein the second vias are aligned with and connected to corresponding ones of the first vias, wherein of one the first and second semiconductor dies includes an operable microfeature device and the other does not.
 17. The semiconductor device package of claim 16 wherein the operable microfeature device is an integrated circuit formed in the semiconductor substrate of the first die.
 18. The semiconductor device package of claim 16 wherein the operable microfeature device includes at least one of an integrated circuit, a capacitor, and a sensing element, but does not include bond pads, conductive lines, or vias.
 19. The semiconductor device package of claim 16 wherein each of the first vias projects beyond the semiconductor substrate of the first die and toward a corresponding one of the second vias.
 20. The semiconductor device package of claim 19 wherein each of the second vias projects beyond the semiconductor substrate of the second die and toward a corresponding one of the first vias. 